Cytotoxicity of rabbit blood for Listeria monocytogenes

Our plain-English summary of Cytotoxicity of rabbit blood for Listeria monocytogenes, by L.D. Shultz, M.S. Wilder (Infection and Immunity, 1971).

The study

• Authors: L.D. Shultz, M.S. Wilder
• Journal: Infection and Immunity
• Published: 1971;4(6):703-8
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Our studies reveal that normal rabbit blood contains a potent bactericidin active against Listeria monocytogenes. The factor is present in greatest amounts in fresh undiluted serum but is absent in platelet extracts. A correlation was observed between the virulence of Listeria strains and their relative ability to survive in serum. The bactericidal titers obtained for plasma and plasma serum indicate that clotting must occur for optimum expression of antilisterial activity. The lethal action is not elevated after immunization with viable Listeria nor does it appear to depend on heat-labile components of complement. The active factor was removed from serum by filtration through a cellulose asbestos filter pad and further purified by carboxymethyl cellulose chromatography. Iron significantly diminishes serum lethality and completely abolishes the action of the purified component. The listericidal factor resembles beta-lysin but may be a distinct part of a multiple system of similar bactericidins.

In plain English

This laboratory study is not about asbestos as a health hazard. Asbestos appears only as a filter used in the experiments. The authors tested whether blood from adult female New Zealand White rabbits could kill the bacterium Listeria monocytogenes in test tubes. Fresh rabbit serum killed all three Listeria strains tested, and the most virulent strain, A4413, was more resistant to serum than the less virulent strains. Serum kept its killing activity after heating at 56 C but lost it at 65 C. Immunizing rabbits with live Listeria raised antibody (agglutinin) titers to 1:640 by day 29, while the serum's bactericidal titer stayed at 32 units/ml. Platelet extract showed no activity, and serum was more active than plasma. Passing serum through an asbestos filter pad removed the killing activity. The factor was recovered from the pad and purified until it was 1,445-fold more active per milligram of protein than serum. Added iron reduced the killing, especially by the purified factor. The authors concluded the factor resembles beta-lysin but may be a distinct, similar bactericidal system.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: laboratory (test-tube) experiments on rabbit blood components and Listeria bacteria
• Who was studied: blood from adult female New Zealand White rabbits (number not stated), tested against three Listeria monocytogenes strains (A4413, the virulent strain; JHH, less virulent; 9037-7, a rough variant) and Bacillus subtilis ATCC 6633; University of Massachusetts, Amherst
• Exposure: No asbestos exposure was studied. An asbestos sterilizing filter pad (Seitz, type C-5) was used only as laboratory equipment to remove the bacteria-killing factor from serum and help purify it.
• Main results:
  • Fresh rabbit serum killed all Listeria strains. The virulent strain A4413 (titer 32 units/ml) was more resistant than strains 9037-7 and JHH (64 units/ml each).
  • Serum activity was fully retained after 30 min at 56 C but lost at 65 C.
  • In immunized rabbits, agglutinin titer reached 1:640 by day 29 while the bactericidal titer stayed constant at 32 units/ml.
  • Platelet extract had no activity against Listeria. Serum was more active than plasma, suggesting the clotting process enhances activity.
  • Serum passed through the asbestos filter pad lost measurable antibacterial activity. The purest purified fraction had specific activity 1,445-fold higher than serum.
  • Iron reduced killing. In serum, 100 micrograms of iron per ml was needed for a significant decline (32.30% bacterial survival). With the purified factor, 10 micrograms per ml allowed about 20% survival (19.50%), and 25 micrograms per ml or more allowed 100% survival.
• The authors' conclusion: The authors concluded that normal rabbit blood contains a potent bactericidin active against L. monocytogenes, resembling beta-lysin but possibly a distinct, similar blood bactericidal system. They also concluded that a correlation may exist between strain virulence and resistance to serum.
• Limitations the authors state:
  • The authors stated that additional studies are required to determine why clotting enhances the activity: either essential substances are released or inhibitors are removed.

Topics

Medical terms in this study, explained in our Lexicon: Filter pad.

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